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Re: CNAMEs for MX



On Tue, Oct 02, 2001 at 12:06:53AM +0200, martin f krafft wrote:
> can someone explain to me, why BIND 9 complains when you list CNAMEs
> as MX records for hosts? i seem to recall that one should not, but:

<snip>

>    There is one other special case.  If the response contains an
>    answer which is a CNAME RR, it indicates that REMOTE is actually an
>    alias for some other domain name. The query should be repeated with
>    the canonical domain name.

It's right there in the last sentence.  The request will be canonized.
It's bad because an extra DNS lookup must be performed to get the A
record for the host.  BIND < 9 has also always complained.  For example:

Oct  1 00:05:48 mintaka named[181]: "optonline.net IN MX" points to a
CNAME (mail-hub.optonline.net)

> according to the RFC, this is not a problem and should be handled
> just perfectly...
> 

It is only treated as a warning, unless BIND 9 has decided to elevate
the severity to an actual error.  The mail gets delivered to the same
place it would had the MX pointed to an A name, though, so there's
nothing to be gained by listing CNAMEs.

noah

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